Avoid setting null system properties in Mojos

Empty values injected by @parameter in a Map are going to be null.
We should avoid trying to push these values to the system properties as
they are ultimately backed by a CHM, which doesn't support null values.

Fixes #47446

Author: gsmet

devtools/maven/src/main/java/io/quarkus/maven/BuildMojo.java

@@ -114,6 +114,10 @@ protected void doExecute() throws MojoExecutionException {
             // Add the system properties of the plugin to the system properties
             // if and only if they are not already set.
             for (Map.Entry<String, String> entry : systemProperties.entrySet()) {
+                if (entry.getValue() == null) {
+                    continue;
+                }
+
                 String key = entry.getKey();
                 if (System.getProperty(key) == null) {
                     System.setProperty(key, entry.getValue());

devtools/maven/src/main/java/io/quarkus/maven/RunMojo.java

@@ -43,6 +43,10 @@ protected void doExecute() throws MojoExecutionException, MojoFailureException {
         // Add the system properties of the plugin to the system properties
         // if and only if they are not already set.
         for (Map.Entry<String, String> entry : systemProperties.entrySet()) {
+            if (entry.getValue() == null) {
+                continue;
+            }
+
             String key = entry.getKey();
             if (System.getProperty(key) == null) {
                 System.setProperty(key, entry.getValue());